Correlation of TGF-(si expression with medroxiprogesterone acetate responsiveness in mouse mammary adenocarcinomas

We investigated the expression of transforming growth factors β₁ and α (TGF-β₁, TGF-α in hormone-responsive (MPA-R) and unresponsive (MPA-U) tumor lines obtained from medroxyprogesterone acetate (MPA)-induced mammary adenocarcinomas in BALBIc mice. The tumors were transplanted into MPA-treated and untreated mice. TGF-β₁ gene expression was observed in the MPA-R lines growing in untreated animals, but not in MPA-treated mice. TGF-β₁ mRNA was not detected in the MPA-U tumor lines growing in either MPA-treated or untreated animals. In MPA-R lines the levels of TGF-β₁ expression were inversely correlated to growth rate. High-affinity TGF-β₁ receptors were present in the MPA-R tumors. These results suggest that one of the mechanisms by which MP A exerts its proliferative effect on MPA-R tumor lines is inhibition of the expression of TGF-β₁. Thus, the lack of expression of TGF-β₁ in MPA-U tumors may be related to the acquisition of autonomous growth.